I'm typing fast as I don't have much time -
Keep in mind that with ANY firearm, YOU are personally responsible for EVERY projectile that comes out of it.
We could get into a discussion about defensive shootings and how projectiles work. What you see in the movies is false. The bad guy doesn't fly backwards 200 feet, or explode. Shotguns don't do that. Handguns don't do that. Shot placement is critical. Forget "stopping power".
In most shooting situations, Projectiles make holes that bleed. Enough blood loss results in Loss Of Consciousness (LOC), they pass out. Making big holes in things that bleed a lot is faster.
In the real world, the bad guy either won't realize he was shot, or he will run off once he hears shots. If he was hit, he may pass out some distance away. Without medical help, he will bleed out. Might happen anyway depending on the internal damage.
In the real world, you don't see police rush up to someone that was shot. Why?
When you pass out, you hit the ground. When you go horizontal, BP comes back up - LOC solved. That person can be a threat again. It also takes a while for BP to drop and LOC to happen. The bad guy can hurt you until he is down. There are videos of police shooting a person multiple times and he doesn't even act like he was hit. That's real world.
I wanted to get that out of the way so that we can talk about appropriate firearms.
You hear people big on shotguns. Shotguns generally fire a lot of little projectiles to take out little things (birds). They are NOT ideal for defense. Why?
Humans are not little. The holes won't be big enough to do much unless at CLOSE range, and you don't want to be that close. LOC takes time, and odds are you won't hit any CNS components that will result in a rapid down.
You are also responsible for every projectile. All of those pellets. They spread out pretty fast.
A few years ago, I was invited to a session with the Taurus Judge and many types of ammo. It was designed with carjackings in mind, and at that range it's great. Beyond from the end of the barrel to the passenger window - a couple of feet - spread means those projectiles may hit bystanders/other property.
Some say "they are less effective at distance". True, but they can still cause injury that you will pay for.
Handguns are popular because they are easily concealed, but they don't have "stopping power". They make holes that bleed. They are a tradeoff. Shot placement is critical.
.50BMG? Now you have stopping power. You can't conceal that or maneuver it in your RV to use it.
Personally, I recommend something shoulder supported that's designed to limit over-penetration yet make holes that bleed a lot AND be easily maneuverable in tight spaces. My favorite is the FN PS90.
http://rvgunner.com/ps90.htm